Added MANIFEST.in to ensure Cython, C++, and Rust sources (.pyx, .pxd, .cpp, .hpp, .c, .h, .rs) are included in the source distribution.
Included runtime dataset files (river/datasets/*, river/drift/datasets/*, river/stream/*.zip) in the source distribution so packages installed from sdist (e.g. via conda-forge) can load bundled datasets.
Added Cargo.lock to the repository and the source distribution for reproducible Rust builds.
Dropped the unused [[bench]] section from Cargo.toml.